146 research outputs found
Final State Radiative Effects for the Exact O(alpha) YFS Exponentiated (Un)Stable W+W- Production At and Beyond LEP2 Energies
We present the LL final state radiative effects for the exact O(alpha) YFS
exponentiated (un)stable WW pair production at LEP2/NLC energies using Monte
Carlo event generator methods. The respective event generator, version 1.12 of
the program YFSWW3, wherein both Standard Model and anomalous triple gauge
boson couplings are allowed, generates n(\gamma) radiation both from the
initial state and from the intermediate W+ W- and generates the LL final state
W decay radiative effects. Sample Monte Carlo data are illustrated.Comment: 16 pages, 8 figures, 2 table
Discovering Technicolor at Hadron Colliders
Strategies are presented for discovering light, color-singlet technipions
(pi_T) produced in association with a vector boson through s-channel technirho
production, at the Tevatron and LHC. Signal and W+jets background were
simulated including detector effects. Tagging of b-quarks from the pi_T -> bb
decay is found to be important to reduce the W+jets background. Kinematic
properties of signal and background events are significantly different and
simple cuts can be used to further improve the signal to background ratio.Comment: 4 pages, 6 figures, LaTeX; to appear in the Proceedings of the 1996
DPF/DPB Summer Study (Snowmass 1996
Direct reconstruction of dynamical dark energy from observational Hubble parameter data
Reconstructing the evolution history of the dark energy equation of state
parameter directly from observational data is highly valuable in
cosmology, since it contains substantial clues in understanding the nature of
the accelerated expansion of the Universe. Many works have focused on
reconstructing using Type Ia supernova data, however, only a few studies
pay attention to Hubble parameter data. In the present work, we explore the
merit of Hubble parameter data and make an attempt to reconstruct from
them through the principle component analysis approach. We find that current
Hubble parameter data perform well in reconstructing ; though, when
compared to supernova data, the data are scant and their quality is worse. Both
CDM and evolving models can be constrained within at
redshifts
and even at redshifts 0.1 z 1 by
using simulated data of observational quality.Comment: 25 pages, 11 figure
Dynamical Dark Energy or Simply Cosmic Curvature?
We show that the assumption of a flat universe induces critically large
errors in reconstructing the dark energy equation of state at z>~0.9 even if
the true cosmic curvature is very small, O(1%) or less. The spuriously
reconstructed w(z) shows a range of unusual behaviour, including crossing of
the phantom divide and mimicking of standard tracking quintessence models. For
1% curvature and LCDM, the error in w grows rapidly above z~0.9 reaching
(50%,100%) by redshifts of (2.5,2.9) respectively, due to the long cosmological
lever arm. Interestingly, the w(z) reconstructed from distance data and Hubble
rate measurements have opposite trends due to the asymmetric influence of the
curved geodesics. These results show that including curvature as a free
parameter is imperative in any future analyses attempting to pin down the
dynamics of dark energy, especially at moderate or high redshifts.Comment: 5 pages, 2 figures. To appear in JCA
Symmetry Restored in Dibosons at the LHC?
A number of LHC resonance search channels display an excess in the invariant
mass region of 1.8 - 2.0 TeV. Among them is a excess in the fully
hadronic decay of a pair of Standard Model electroweak gauge bosons, in
addition to potential signals in the and dijet final states. We perform a
model-independent cross-section fit to the results of all ATLAS and CMS
searches sensitive to these final states. We then interpret these results in
the context of the Left-Right Symmetric Model, based on the extended gauge
group , and show that a heavy right-handed
gauge boson can naturally explain the current measurements with just a
single coupling . In addition, we discuss a possible connection
to dark matter.Comment: 25 pages, 12 figures, V2: references added, extended discussion of
Minimal Left-Right Dark Matter, small correction to decay width - conclusions
unchanged, V3: expanded discussion of input parameters and statistical
procedure, V4: matches published versio
Helicity-dependent cross sections and double-polarization observable E in η photoproduction from quasifree protons and neutrons
Precise helicity-dependent cross sections and the double-polarization observable E were measured for η
photoproduction from quasifree protons and neutrons bound in the deuteron. The η → 2γ and η → 3π0 → 6γ
decay modes were used to optimize the statistical quality of the data and to estimate systematic uncertainties. The
measurement used the A2 detector setup at the tagged photon beam of the electron accelerator MAMI in Mainz.
A longitudinally polarized deuterated butanol target was used in combination with a circularly polarized photon
beam from bremsstrahlung of a longitudinally polarized electron beam. The reaction products were detected with
the electromagnetic calorimeters Crystal Ball and TAPS, which covered 98% of the full solid angle. The results
show that the narrow structure observed earlier in the unpolarized excitation function of η photoproduction off
the neutron appears only in reactions with antiparallel photon and nucleon spin (σ1/2). It is absent for reactions
with parallel spin orientation (σ3/2) and thus very probably related to partial waves with total spin 1/2. The
behavior of the angular distributions of the helicity-dependent cross sections was analyzed by fitting them with Legendre polynomials. The results are in good agreement with a model from the Bonn-Gatchina group, which
uses an interference of P11 and S11 partial waves to explain the narrow structure
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